So I have a lovely little fancy goldfish named Virgil, and he has symptoms of this infection which is what I believe to be Septicemia or sometimes nicknamed Red Pest. I've had him for about 6 months, and I suspect he may have had this infection since I bought him because I remember seeing traces of it early on but didn't understand the sign yet. He's had a couple outbreaks of it where it got really bad-- tail and belly covered in vein-y red hemorrhages and he acted real ill-- but he pulled through each time with the help of some fish medicine, an each outbreak was weaker than the next. My trouble is though, that the infection doesn't seem to truly go away. He still had very strong red hemorrhage running down his tail fin.

I treated with hydrogen peroxide bath the first outbreak, since I felt a little wary of medicating him, but then I resorted to using API's E.M. Erythromycin. A month or so later, he had a second outbreak. So, I tried Jungle's Fungus Clear which at first seemed to knock the infection out, but when he developed a third outbreak, and I tried using it again, it seemed less effective and stressed Virgil out too much.
So I did some research and found SeaChem's KanaPlex, which seemed gentle enough on Virgil's system and has made the ugly red vein dramatically fade to a soft pink--- yet it is still there...oof.

So I need advice, I know internal infections are hard to treat, but this little goldfish is real resilient and I think he can pull through if I take the right steps. Does anyone here have experience with Septicemia and have a better suggestion for antibiotics? Can an infection like this ever go away completely? Also, how long should you treat your fish with medicine? I feel like I have really gone overboard, but I only treat it when the symptoms are worsening, and I try to leave him alone when its getting better or remaining the same. I try to give him at least a week long break between treatments, but the infection came back so fast I had to put him on KanaPlex a bit sooner than I thought.